The Impact of Plant-Derived Foods and Medicines on the Lung–Gut Axis and Microbiota Cross-Talk

The gut–lung axis is one of the bidirectional mucosal communication networks linking intestinal microbiota, microbial metabolites, immune regulation, and respiratory inflammation. This narrative review summarizes mechanistic and translational evidence identified through a structured but non-systematic search. This review focuses on gut-to-lung mechanisms, including immune cell trafficking, epithelial barrier regulation, and the role of gut microbiota and its metabolites. Among these metabolites, short-chain fatty acids (SCFAs), particularly acetate, propionate, and butyrate, are key mediators of interorgan communication and are mainly produced through microbial fermentation of dietary fibers and polysaccharides. Unlike previous reviews, reverse lung-to-gut mechanisms are also discussed, whereby respiratory infection, smoking, and lung injury may disrupt intestinal barrier integrity, alter gut microbiota composition, and promote intestinal immune dysregulation. Among plant-derived interventions, dietary fibers, polysaccharides, and polyphenols appear promising, mainly through SCFA-dependent immune modulation, enrichment of metabolite-producing bacteria, and subsequent suppression of inflammatory pathways. Some compounds may also act through microbiota-independent mechanisms, including direct antioxidant effects, epithelial barrier protection, and inhibition of inflammatory signaling pathways. Overall, SCFA-mediated immune regulation is the best-supported mechanism, whereas lung-to-gut signaling remains less established. Most evidence remains preclinical, highlighting the need for standardized human studies evaluating dose, safety, and clinically meaningful respiratory outcomes.